Method and apparatus for treating lamp filaments



April 29, 1958 E. H. WILEY 2,832,661

METHOD AND APPARATUS FOR TREATING LAMP FILAMENTS Filed Jan. 18, 1956 2 Sheets-Sheet 1 lnven tov'.

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METHOD AND APPARATUS FOR TREATING LAMP FILAMENTS Filed Jan. 18, 1956 2 Sheets-Sheet 2 Invervtov: Emmett H. WiLeg,

5 His Ag e United States Patent M METHOD AND APPARATUS FOR TREATING LAMP FILAMENTS Emmett H. Wiley, East Cleveland, Ohio, nssigllor to General Electric Company, a corporation of New York Application January 18, 1956, Serial No. 559,803

8 Claims. (Cl. 316--1) My invention relates to electric lamps and similar devices comprising an envelope or bulb containing a filament of refractory metal such as tungsten, and more particularly to a method and apparatus for setting the filament.

The physical properties of tungsten wire as used in incandescent lamps vary considerably with working and with heat treatment. The drawn wire used for coiled filaments has a fibrous structure which gives it the ductility required for the coiling operation. That structure must be changed at some stage of lamp manufacture to one of large crystals which has been found to give the desired strength against sagging at high temperatures. The change is accomplished by heating the filament coil to a temperature of recrystallization; usually the filament is heated to approximately 3200 K. Ordinarily this is done as the first lightup of the sealed lamp and is called flashmg.

When the flashing treatment is accomplished by lighting up the sealed lamp, some provision must be made to prevent the deformation or sagging of the coil during the hot interval before the strong structure is obtained inasmuch as the rigidity of the Wire at the flashing temperature is rather low until the desired crystalline structure has had time to grow.

The problem is particularly acute in lamps which have one or more relatively long lengths of the coiled filament extending between support members. One lamp of that type is a quartz infrared lamp recently introduced on the market and which has a long coiled filament extending axially in a tubular envelope with supporting disks of tantalum affixed to the coil at spaced intervals and resting freely on the inside of the envelope. The coil must be in the ductile condition at the time the support disks are .afiixed thereto in order to prevent breakage of the coil. Certain other types of lamps having long axial filament cells have been flashed heretofore by raising the voltage across the filament in successive steps while rotating the lamp about its axis in a horizontal position. However, that method proved to be unsuitable for the quartz infrared lamp referred to above on account of the fact that the endmost segments of the filament were distorted. This was found to be due to the fact that the disk supports are.attached to the coil and they tend to roll on the envelope during the rotation of the lamp. Since the ends of the coil are fixedly held by respective lead-in wires the rolling action causes one end segment of the coil to unwind and the other end to wind tighter.

. in accordance with the present invention, the problem is solved by flashing the filament while the lamp is undergoing acceleration such that it is in a state approximating free fall, thereby efiectively nullifying the effect of gravity on the filament so that it has no tendency to sag. Since the unset coil does have some degree of hot strength or rigidity it is not necessary to completely cancel the force of gravity thereon. On the other hand, it is desirable in some cases to subject the filament to an effectively 2,832,661 Patented Apr. 29, 1958 that the coil is actually bowed upward somewhat, particularly when the time interval for flashing is so short that the filament is not completely recrystallized; the recrystallization may then be completed by heating the filament for an additional interval while the lamp is at rest, whereby the filament sags slightly to a straight position.

Further features and advantages of my invention will appear from the following detailed description and from the drawings wherein:

Fig. 1 is a side view of a lamp which may be treated in 1 accordance with the invention;

downward acceleration greater than that due to gravity so Fig. 2 is a diagram of a path through .whichthe lamp may be moved in practicing the invention;

Fig. 3 is a graph illustrating the relationship of force vs. time of a lamp traveling the path of Fig. 2;

Fig. 4 is a graph illustrating the position above point a of Fig. 2 with respect to time;

Fig. 5 is a graph illustrating force vs. time of a modified arrangement;

Fig. 6 is a graph illustrating the actual position vs. time curve of a practical device in comparison with a theoretically desirable parabolic curve;

Fig. 7 is a somewhat diagrammatic elevation of a simplified mechanism for practicing the invention;

Figs. 8 and 9 are front and side views, respectively, of a mechanism suitable for practicing the method in accordance with my invention; and I Fig. 10 is a schematic line diagram of the electrical circuit employed in the device shown in Figs. 8 and 9.

It will be evident that from a practical standpoint free fall cannot be maintained for very long periods of time because the distances become prohibitively large. The distance is, of course, governed by the relationship S= /2gz where S is the distance traveled in free fall from rest in time t, and g is the a'cceleration due to gravity. If S is measured in feet and tin seconds, g has a value of about 32 ft./sec./sec., so that S: 16 t For one second of free fall S is 16 ft. and the object would be moving at a velocity of V=gt=32 ft./sec.

It will therefore be seen that in order to obtain a one second interval of free fall in which to flash the filament, the lamp must be allowed to travel 16 feet plus the distance required to bring it to a stop smoothly enough to prevent damage. However, the free fall need not be from an initial condition of rest. If the lamp is projected upwardly, instead of being dropped from rest, the path can be essentially folded with a resultant reduction of the required track length to one-fourth. For a period of free travel of one second, the length of the course would then be only four feet. The distance required to give the lamp its projected velocity would be the same as the stopping distance for the same maximum force on the lamp, so that the total track or course height would be twice the length of the free fall region.

A typical path would then be as shown in Fig. 2 wherein ab is the region wherein the lamp is accelerated vertically to the velocity required to carry it to a height above point b equal to bc before it comes to a stop and begins to fall back to point d where braking or deceleration begins to bring it to a uniform stop at point e which is coincident with point a, its starting position. The lamp is in a state of free fall through the combined region bed. In this example ab=bc=cd=de; that is, the object is accelerated over the regions ab and de upwardly at a rate equal to that of gravity. The force on the object in these two regions is then the force due to gravity plus the force due to the acceleration (in this case equal to that of gravity) or a total of twice the force of gravity.

The relationship of force vs. time would be as shown in C3 are semi-parabolas opening upwardly whereas the region bed is a parabola opening downwardly.

In Fig. 1 I have illustrated one type of lamp for which the invention is particularly useful, although it will be understood that the method is applicable to any type of lamp having relatively long unsupported lengths of filament. The lamp of Fig. l is of the quartz infrared type disclosed and claimed generally in application Serial No. 376,042 Foote et al. and comprising an elongated tubular envelope 1 of quartz containing a gas filling at about atmospheric pressure and having a coiled tungsten filament 2 extending axially thereof and connected at its ends to molybdenum lead-in wires 3 having flattened intermediate portions 4 hermetically sealed in flattened press or seal portions 5 at the ends of the envelope. The filament 2 is supported at spaced points along its length by tantalum discs 6 of slightly smaller diameter than the inner diameter of the envelope and which may be secured to the filament as disclosed in applications Serial Nos. 456,674 and 456,831, both filed September 17, 1954 by E. G. Fridrich.

In Fig. 7 I have illustrated a simplified mechanism for carrying out the invention. The device comprises a vertical rail or track 10 which may be made of a T-shaped metal member formed by bolting together a pair of angle irons. The lamp 1 is mounted on a carriage 11 comprising a plate member 12 on which are mounted pairs of pulleys 13 straddling the rail 10. The plate 12 carries a cross piece 14 on which are mounted a pair of socket members 15 for supporting the lamp 1 and making electrical connection thereto. A resettable switch 16 is mounted on the stern portion of the T-shaped rail 10 in position to be tripped to its closed position by a projection or finger member (not shown) on the carriage 11. The lamp 1 is connected to the terminals 17, 18 of a source of current supply through a timer l9 and the switch 16.

To flash the lamp, the carriage 11 is propelled upwardly along the traclg 10, either manually or by a suitable propelling device such as a spring, past the switch 16 which is actuated to its closed position by the carriage 11, thereby connecting the lamp 1 with the power supply 17, 18. At a predetermined interval in the return downward travel of the carriage 11, the power to the lamp is turned off by the timer 19, and the carriage is caught as gently as possible and brought to rest against a stop 20.

The switch 16 is located to be approximately at a point corresponding to 11in Fig. 2 when the lamp is in a state of free fall, and the timer 19 is adjusted to turn oil the power before the lamp reaches a point corresponding to d in Fig. 2, i. e., before the end of the free fall period, so that the filament is permitted to cool down before it is again subjected to the force of gravity and deceleration, thereby preventing bowing or sagging of the filament. The operation may then be repeated to fully set the filament. While manual operation, of course, does not provide uniform acceleration and deceleration, it does provide an interval of free fall in which to flush the lamp and has been found to be very efifective in obtaining a straight filamentcoil.

In designing a device more suitable for production purposes, it is not necessary to duplicate precisely the motion represented by Figs. 24. Therefore, instead of providing a device that will generate parabolic motion, it is sufiicient to provide the close approximation thereof afforded by simple harmonic motion, or sinusoidal motion. One such device is illustrated in Figs. 8 and 9 wherein the lamp ismoved up and down along a vertical path to describe one cycle of simple harmonic motion wherein the displacement as a function of time is given by the equation S: S; cos.

where T is the time of one complete cycle and S is the amplitude of the motion. The total force acting on the lamp, including that due to gravity (g) is F (as te m 2 g 31 cos (l-jt-i-g If S is chosen such that then the force is represented by the solid line curve 21 of Fig. 5 and the displacement vs. time is represented by the solid line curve of Fig. 6, the dotted line curve being that of Fig. 4 for comparison. The dotted line curve 22 applies for a choice of S; which is slightly larger. Thedot-dash line 23 is that of Fig. 3 and is included for comparison. Since the sinusoidal ctu've is only an approximation of the free fall curve, a value of S is chosen such that the departure tends to average out to some extent; that is, 8 is chosen to give values line the dotted line curve 22 wherein The mechanism which generates this motion is coupled to a circuit which applies voltage to the lamp at approximately point b of Fig. 5. This filament is raised to its setting or recrystallization temperature approximately at point b and remains thus to point e where the power to the lamp is turned oil. 4 The region cd allows the filament to cool to a sufficiently low temperature to withstand the forces of deceleration from d to e. The portions of the curve b to d may be thought of as the high temperature part of the cycle. During part of this region a residual force tends to sag the coil downward while over the other part of this region the residual force is upward. The amount of residual upward force at the top position is determined by the choice of S as discussed above.

It should be remembered that the unset coil does have some hot strength or rigidity such that complete elimination of force is not necessary, especially since the slight tendency to sag during the light-up interval b'c' can be averaged out by the proper choice of 8,. Moreover, adjustment of the position of the light-up interval bc along the cycle will vary the ratio of upward sag to downward sag in moving along the curve 22 of Fig. 5. In the device illustrated in Figs. 8 and 9 the time for one cycle is nearly one second so that the light-up in terval b'c' is about one-quarter of a second. Since the coil reaches a high temperature very quickly at the lightup voltage, this interval is long enough to provide sufficient crystallization and strength to permit completing the crystallization under the full force of gravity. This may be accomplished by lighting up the filament for about 5 to 10 seconds at the setting temperature after the cycle has been completed.

Referring more particularly to the structure of the device shown in Figs. 8 and 9, the lamp 1 is supported in a horizontal position by a horizontal carrier in the form of a channel or bracket 30 carrying a pair of sockets 31 having terminals (not shown) for engaging the ends of the lamp and making electrical connection to the respective lead-in wires 3 thereof. The bracket 30 is moved upwardly and downwardly along a vertical path in approximately simple harmonic motion by a pair of arms or links 32 and 33 which are pivotally interconnected at one end by a hub or shaft 34; the other end of the primary link 32 is mounted for rotation on a hub or shaft 35 and the other end of the secondary link 33 carries the bracket 30 through a hub or shaft 36. The link 32 is rotated (counter-clockwise, as viewed in Fig. 8) by v 7 an electric motor 37 through a reduction gear assembly 38 and shaft 39 (Fig. 9) which is fixed to the hub 35 which is, in turn, fixed to the link 32.

While the link 32 is being rotated through one revolution the end of link 33 carrying the hub 36 and bracket 30 is constrained to move upwardly and downwardly along a vertical line by virtue of the chain 40 which is wrapped around a stationary sprocket 41 concentric with the hub 35, and around a sprocket 42 which is fixed to the hub 34 which is rotatably mounted in the end of link 32 and is fixed to the link 33. The sprocket 41 is secured to a stationary bracket 43 attached to the support 44 which also supports the motor 37. The bracket 30 is prevented from freely pivoting with its hub 36 in the end of link 33 by a chain 45 which is wrapped around a sprocket 46 fixed to the end of link 32, and around a sprocket 47 fixed to the hub 36. In the illustrated device the links 32 and 33 are of the same length and the sprockets 41 and 47 are in a ratio of 2 to 1 to the sprockets 42 and 46.

To start the device into operation, a switch A (Fig. is closed. This energizes a relay coil To in a process timer T (having contacts T1 and T2) by connecting one terminal 50 of a power supply through conductors 51 and 52, switch A, conductor 53, coil To and conductors 54, 55 and 56 to the other terminal 50' of the power supply. First the contacts T1 close, thereby energizing a. relay coil Rc through the normally closed contact K1 and conductors 57 and 58. The coil Rc causes its contacts R3 and R4 to open and contacts R1 and R2 to close and thereby start the motor 37 through its cycle.

At the start of the operation, a normally closed microswitch B is held open by a cam 59 mounted on the hub 35, and after about 90 degrees of rotation of the hub 35, the cam 59 permits the switch B to close, and shortly thereafter the contacts T1 are opened by the timer. It is only necessary that the contacts T1 open some time after the switch B closes. The cam 59 is designed to open switch B at the point in the cycle necessary to cause the lamp carrier or bracket 30 to come to rest at its lowermost position. Since the particular motor 37 employed tended to coast somewhat, the cam 59 was set to open the switch B at about 270 or three-quarters of the complete rotation of the hub 35. It will be seen that switch T1 starts the cycle of the motor 37 and switch B stops it. That arrangement prevents wandering of the rest position.

As illustrated herein the circuit also includes a relay having a coil K and contacts K1, K2 and K3 because the timer T actually employed had too large a range to be easily adjusted to a point between the closing and opening of switch B. Since the contacts K1 open when the microswitch D closes and remain open for the rest of the cycle, the opening of contacts T1 need occur only some time after switch B closes. When coil K is energized through contacts K3 and switch D, the contacts K2 close and contacts K3 open, thereby keeping coil K energized until switch A is opened.

. Since the motor 37 tended to coast excessively, braking of some sort was provided. This was accomplished dynamicaly by applying a D. C. voltage to the motor at the moment the A. C. voltage is removed. With a squirrel cage motor 37 this may be effected by employing a variable D. C. current supply comprising a variable auto transformer 60, a step down transformer 61, and a full wave rectifier 61', and connected across the motor 37 through the contacts R3 and R4. The opening of the cam-actuated switch B de-energizes the relay coil Re which causes the contacts R3, R4 to close and the contacts R1, R2 to open, thereby completing the cycle of the motor 37.

The lamp light-up is effected by the normally open microswitch D which is controlled by a cam 65 on the hub 35 to turn power to the lamp on and off at the proper time. After about 90 of rotation of the hub 35 and cam 65, the switch D is closed to thereby energize the relay coil N which closes its contact N1 to supply power to the transformer 66 and to the lamp 1 through the conductors 67 and 68. After about rotation from rest, the switch D is again opened by cam 65 to turn off the power to the lamp.

Power to the lamp is turned on when the carrier reaches theelevation of hub 35. The carrier then continues to its uppermost position shown by dot-dash lines at 30', and power is turned ofi when the carrier reaches the position shown by dot-dash lines at 30".

After the lamp has gone through its cycle it may be lighted for an additional period of some 5 to 10 seconds to further complete the recrystallization of the filament. This is accomplished by proper setting of the timer T to cause the contacts T2 to close after the motor 37 has stopped and to remain closed for the desired interval. I

While I have shown and described certain specific apparatus for effecting the process in accordance with my invention it will be apparent to those skilled in the art that the apparatus may be widely modified within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent on the United States is:

1. In the manufacture of an electric lamp comprising an envelope containing a coiled metallic filament having a substantial unsupported length, the method of setting the said filament which comprises flashing it to a temperature of recrystallization while the lamp is undergoing acceleration'such as to at least partly cancel the force of gravity on the filament.

2. In the manufacture of an electric lamp comprising an envelope containing a coiled metallic filament having a substantial unsupported length, the method of setting the said filament which comprises flashing it to a temperature of recrystallization while subjecting the lamp to acceleration approximating a state of free fall.

3. In the manufacture of an electric lamp comprising an envelope containing a coiled metallic filament having a substantial unsupported length, the method of setting the said filament which comprises moving the lamp upwardly and downwardly along a vertical path at a variable rate of speed approximating simple harmonic motion, and flashing the filament to a temperature of recrystallization during an interval in which the acceleration of the lamp is such as to approximate a state of free fall.

4. In the manufacture of an electric lamp comprising an envelope containing an elongated coiled metallic filament having a substantial unsupported length, the

method of setting the said filament which comprises flashing the filament to a temperature of recrystallization while maintaining the lamp with its filament in a horizontal position and moving it along a vertical path at an acceleration such as to at least partly cancel the force of gravity on the filament.

5. In the manufacture of an electric lamp comprising an envelope containing a coiled tungsten filament having a substantial unsupported length, the method of setting the said filament which comprises subjecting the lamp to an eflectively downward acceleration greater than that due to gravity and simultaneously flashing the filament to a temperature of recrystallization for a brief interval insutficient to effect complete recrystallization, and then bringing the lamp to rest and reheating the filament for a time sutficient to effect virtually complete recrystallization. I

6. Apparatus for setting the metallic filament of an electric lamp comprising a holder member including con tact means for supporting the lamp and making an electrical connection to the filament, means for moving said holder member along a vertical path and at an acceleration such as to at least partly cancel the force of gravity on the filament of the lamp carried thereby, a source of electrical energy capable of supplying to said filament a current sufficient to heat it to a temperature of recrystallization, and means for connecting said filament through said contact means with said source of electrical energy for a time interval during which the filament is moving along said path at the said acceleration.

7. Apparatus for setting the metallic filament of an electric lamp comprising a holder member including contact means for supporting the lamp and making an electrical connection to the filament, means for moving said holder member upwardly and downwardly along a vertical path at a variable rate of speed approximating simple harmonic motion and at an acceleration such as to approximatea state of free fall over a portion of said path, a source of electrical energy capable of supplying to said filament a current sufficient to heat it to a temperature of recrystallization, and means for connecting said filament through said contact means with said source of electrical energy for a time interval during which the said holder and the lamp therein are in the state of free fall.

8. Apparatus for setting the metallic filament of an electric lamp comprising a horizontally disposed holder member including contact means for supporting a lamp with its filament in a horizontal position and making electrical connection thereto, mechanism for moving said holder member upwardly and downwardly along a vertical path at a variable rate of speed approximating simple harmonic motion and at an acceleration such as to approximate a state of free fall over a portion of said path, said mechanism comprising a rotatable horizontal shaft, means for rotating saidshaft about its axis, a primary link extending laterally from said shaft and secured at one end to said shaft for rotation therewith, a first hub rotatably mounted in the other end of said primary link with its axis parallel to the axis of said shaft, a secondary link fixedly connected atone end to said first hub, a second hub rotatably mounted in the free end of said secondary link with its axis parallel to the axes of. said shaft and first hub, said lamp holder member being fixedly supported by said second hub, a stationary first sprocket fixedly mounted concentric with the axis of'said shaft, a second sprocket and a third sprocket concentric with said first hub, said second sprocket being fixed to said second hub, said third sprocket being fixed to said secondary link, a fourth sprocket concentric with and fixed to said second hub, said primary and secondary links being of the same length between their respective pivot axes, said first and fourth sprockets being in a ratio of two to one to said second and thrid sprockets, a first chain wrapped around said first and secondv sprockets and a second chain wrapped around said third and fourth sprockets whereby to constrain the said. lamp holder member to move vertically in simple harmonic motion while maintaining its horizontal position, a source of electrical energy capable of supplying to said holder contacts a current sutficient to heat the filament of the lamp carried thereby to a temperature of recrystallization, and switch means operable upon rotation of said shaft to connect the lamp filament through said contact means with said source of electrical energy for a time interval during which the said holder member and the lamp therein are in a state of free fall.

References Cited in the tile of this patent UNITED STATES PATENTS 1,747,063 Dushman Feb. 11, 1930 1,747,064 Dushman Feb. 11, 1930 1,842,158 Ferguson et al. Jan. 19, 1932 1,897,140 Perez Feb. 14, 1933 1,955,794 DuMont et al. Apr. 24, 1934 2,434,517 Poehler et al Ian. 13, 1948 2,747,961 Coyne, Jr. et al. May 29, 1956 

1. IN THE MANUFACTURE OF AN ELECTRIC LAMP COMPRISING AN ENVELOPE CONTAINING A COLIED METALLIC FILAMENT HAVING A SUBSTANTIAL UNSUPPORTED LENGTH, THE METHOD OF SETTING THE SAID FILAMENT WHICH COMPRISES FLASHING IT TO A TEMPERATURE OF RECRYSTALLIZATION WHILE THE LAMP IS UNDERGOING ACCELERATION SUCH AS TO AT LEAST PARTLY CANCEL THE FORCE OF GRAVITY ON THE FILAMENT. 